Wastewater concentration

ABSTRACT

There are disclosed herein equipment and methods for screening and concentrating waste water overflow from combined sewer systems. Exemplary equipment includes a separator employing a substantially cylindrical rotating screen. Influent is piped upwardly into the equipment and deflected outwardly toward the inner surface of the screen in a manner to achieve a desired flow rate and flow pattern of the influent onto the screen. Means are provided for controlling the flow rate and for suitably directing the influent in a plurality of substantially discrete inclined streams toward the inner surface of the rotating screen. The screen is rotated at a speed to achieve a desired centrifugal force. Effluent passes through the screen to an outlet and the remaining concentrate passes to an outlet. A certain amount of the influent splashes from the inner surface to the screen, and is received by a backsplash pan and may be recirculated and rescreened. The screen is in the form of a screen cage having a plurality of removable screen panels for facilitating replacement of damaged screens or changing of screen type or mesh size. Cleaning means is provided for directing a cleaning fluid periodically at the screen. The methods disclosed involve the manner in which the influent, effluent, concentrate and backsplash are handled, and the manner in which the influent is screened to achieve a fluid concentrate which is pumpable to other treatment equipment for ultimate disposal. Additionally, a sequence of influent food and screen cleaning is described.

United States Pate Talley, Jr- Apr. 17, 1973 WASTEWATER CONCENTRATIONfrom combined sewer systems. Exemplary equipment [75] Inventor: wanTalley, Jr Brentwood includes a separator employing a substantiallycylin- Park, Calm dncal rotating screen. influent lS piped upwardly mtothe equipment and deflected outwardly toward the Assignw Swew, L05 gCalifinner surface of the screen in a manner to achieve a desired flowrate and flow pattern of the influent onto [22] Filed 1971 the screen.Means are provided for controlling the PP 2119763 flow rate and forsuitably directing the influent in a plurality of substantially discreteinclined streams Related Apphcauon Data toward the inner surface of therotating screen. The

[63] Continuation of Ser. No. 42,165, June I, 1970, aban- Screen isrotated at a speed to achieve a desired cloned. trifugal force. Eflluentpasses through the screen to an outlet and the remaining concentratepasses to an out- [52] US. Cl. ..210/377, 210/380 let. A certain amountof the influent splashes from the [51] Int. Cl. ..B0ld 33/02 innersurface to the screen, and is received by a [58] Field of Search..2l0/78, 377, 380 backsplash pan and may be recirculated andrescreened. The screen is in the form of a screen cage [56] ReferencesCited having a plurality of removable screen panels for facilitatingreplacement of damaged screens or chang- UNITED STATES PATENTS ing ofscreen type or mesh size. Cleaning means is pro- 3,511,373 5 1970McKibben et al. "210 380 x vided for directing a cleaning fluidPeriodically at the Primary Examiner-Reuben Friedman AssistantExaminer-F. F. Calvetti Attorney-Lyon & Lyon ABSTRACT There aredisclosed herein equipment and methods for screening and concentratingwaste water overflow 2 Claims, 13 Drawing Figures PATENTED APR 1 7 I975PATENTEI] APR 1 i 1315 SHEET3UF6 PATENTED APR 1 7 I973 SHEET [1F 6WASTEWATER CONCENTRATION This is a continuation of application Ser. No.42,165, filed-June 1, 1970, which is now abandoned.

CROSS REFERENCE TO RELATED APPLICATIONS The concepts disclosed hereinare related to those disclosed in copending application Ser. No.640,241, filed May 22, 1967, now US. patent No. 3,539,008, entitledScreening Apparatus Employing Rotating Cylindrical Screen and StationaryFeed Means," and US. Pat. No. 3,511,373, both of which are assigned tothe assignee of the present application and the disclosures of which areincorporated herein by reference. Briefly, said application Ser. No.640,241 discloses apparatus involving a rotating substantiallycylindrical screen in combination with a stationary distribution meansfor screening an influent. The screen and distribution means may be usedin combination with a downstream planar vibratory separator for furtherscreening of the concentrate from the rotating screen. Said US. Pat. No.3,5ll,373 discloses apparatus similar to that in said application and isdirected to means for facilitating cleaning of said rotating screen.

Reference is also made to related applications, filed concurrentlyherewith, Ser. No. 149,609, entitled Up Flow Separator," filed in thename of Theodore R. Westfall; Ser. No. 210,179, entitled ImprovedRotating Screen Separator, filed in the name of Philip H. Mook; and Ser.No. 126,080 entitled Wastewater Concentration, filed in the names ofWalter J. Talley, J r., and Howard W. Wright, Jr. These applicationscontain a similar disclosure to that set forth herein, but includeclaims directed to various of the structural and operational featuresdisclosed herein.

BACKGROUND OF THE INVENTION This invention relates to the screening of aliquidsolids influent to achieve a desired separation of liquids andsolids, and more particularly to screening of storm water, sewage orstorm water overflow from combined sewer systems.

Although the present inventive concepts are useful in screening variousmaterials, they have particular application for water polution contrbland, thus, will be described in this environment and particularly forfine mesh screening for primary treatment of storm water overflow fromcombined sewer systems. As set forth in a research report on treatmentof storm water overflow entitled Rotary Vibratory Fine Screening ofCombined Sewer Overflows prepared by Cornell, Howland, Hayes andMerryfield in connection with Department of the Interior Contract14-12-128 and dated March 1970, the majority of the existing combinedsewers throughout the nation do not have adequate capacity during heavystorm periods to transport all waste and storm-caused combined flows toa treatment facility. The overflow is bypassed to a receiving stream,thus causing pollution in the nations water courses.

As further described in said report, the Federal Water Pollution ControlAdministration published a report in 1967 reviewing the effects andmeans of correcting combined sewer overflows on a national basis. Of the200 million people residing in the United States, approximately 125million are served by combined or separate sewer systems, and of the 125million, approximately 29 percent are served by combined sewers.Combined sewers are designed to receive all types of waste flows,including storm water, for ultimate treatment at a treatment facility.In determining the size of the combined sewer, it has been commonengineering practice to provide capacity for three to five times thedry-weather flow. During intensive storm periods, how ever, thestorm-caused combined flow may be two to one hundred times thedry-weather flow, making overflow conditions unavoidable. To compoundthe problem, most treatment facilities are not designed to handle thehydraulic load of the combined sewer and, therefore, are required tobypass a portion of the storm-caused combined flow to protect thetreatment facility and treatment process from damage. The nationstreatment facilities bypass flows an estimated 350 hours during theyear, or about 4 percent of the total operation time. The pollutionalimpact of the stormcaused combined overflow of the waters of the nationhas been estimated as equivalent to as much as 160 percent the strengthof the domestic sewage biochemical oxygen demand. This amount creates amajor source of pollution for the nations water courses. The cornell etal. report further describes certain tests, results and recommendationswith respect to the use of high-rate tine-mesh screens for primarytreatment of storm water overflow from combined sewer systems, theequipment described being similar to that disclosed in said applicationSer. No. 640,241 and US. Pat. No. 3,51 1,373. The present inventiveconcepts involve certain improvements thereover.

In light of the foregoing, it is a principal object of the presentinvention to provide improved screening equipment and methods.

A further object of this invention is to provide an improved screeningdevice employing a rotating screen method of screening storm wateroverflow and the like,

deriving a fluid effluent and a suitable flowable concentrate therefrom,and applying the concentrate to a sewer system or the like for treatmentor disposal and causing said effluent to bypass the sewer system toprevent overburdening of the sewer system and pollution of .watercourses.

Other objects and features of the present invention will become apparentthrough a consideration of the following description and attacheddrawings.

SUMMARY OF THE INVENTION There is a disclosed herein a screeningapparatus, such as for use in screening of storm water overflows fromsewer systems, comprising a substantially cylindrical rotary screendevice disposed for rotation within a housing, feed means for directingan influent toward the inner surface of the screen, and outlet means forreceiving (a) the effluent which passes through the screen, (b) theconcentrate which does not pass the screen, and (c) backsplash from thescreen.

The feed means includes an upwardly extending feed pipe, or the like,for supplying the influent to the screen. The feed means may includeadjustable means for varying the rate of flow of influent, and deflectormeans may be provided for directing the flow of influent as a pluralityof substantially discrete inclined streams toward the inner surface ofthe screen.

The rotary screen is in the form of a substantially cylindrical cage andincludes a plurality of screen panels, which may be removed for repair,cleaning or replacement with different mesh screens or different screencloth. The speed of rotation of the screen is selected to provide adesired centrifugal force, or gloading of influent on the screen, theg-loading being a function of the radius of the screen and the square ofthe rpm thereof. The velocity of flow of influent onto the screen isselected within a preferable range below which suitable impingement doesnot occur, and above which excessive splashback and possible screendamage may occur. A typical flow velocity is in a range aroundapproximately 13 to feet per second, and exemplary preferred screenspeeds are approximately 65 rpm for a 60 inch diameter screen and 88 rpmfor a 36 inch diameter screen, it being appreciated that other suitableflow velocities, screen speeds, diameters, and the like may be employedwithout departing from the present concepts.

The influent preferably is screened to achieve a relatively fluidconcentrate, as distinguished from a dry concentrate, so that the samemay be readily transported or pumped for further treatment or disposal;

A screen cleaning apparatus is provided for spraying cleaning fluidthrough the screen at desired intervals. In the screening of aninfluent, it is preferable to cyclically (a) feed the influent for apredetermined period of time, (b) terminate the feed, (c) spray thescreen with a cleaning fluid for a shorter predetermined period, and (d)return the feed of influent. An exemplary cycle includes feedinginfluent for 4% minutes and cleaning the screen for one-half minute,including a cleaning spray from outside to inside of the-screen for afew seconds and then inside to outside of the screen for a few seconds.

Although a complete screening apparatus and methods involving a numberof novel concepts and structures are disclosed herein, this applicationis particularly directed to improved waste water screening conceptsparticularly for screening during heavy storm periods, means forproviding a suitable rate of flow of influent to a rotating screendevice, and cyclic cleaning of the screen of said screening device;whereas said other applications filed concurrently herewith are directedto other novel features disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectionalelevational view of a preferred screening apparatus;

FIG. 2 is a top plan view of the apparatus of FIG. 1;

FIG. 3 is a cross-sectional view of the apparatus taken along a line 3-3of FIG. 1;

FIGS. 4a and 4b are cross-sectional views illustrating an adjustableinfluent plate of the apparatus of FIG. 1;

FIG. 5 is a perspective view of a distribution dome of the apparatus ofFIG. 1;

FIG. 6a is a top view and FIGS. 6b and 6c are fragmentarycross-sectional views of the distribution dome of FIG. 5;

FIG. 7 is a partial perspective view of a rotary screen cage of theapparatus of FIG. 1;

FIG. 8 is a partial top view of the screen of FIG. 7; and

FIGS. 9a and 9b are views illustrating the manner in which screen panelsare secured to the screen cage of FIG. 7.

DESCRIPTION OF PREFERRED EMBODIMENTS Turning now to the drawings, andparticularly to FIGS. 1 through 3, a rotary screening device isillustrated including an outer substantially cylindrical housing 10containing a rotary screen cage 11, an influent inlet feed pipe 12, aninfluent impingement plate or diverter 13, a drive assembly 14 for thescreen cage 11, an effluent outlet 15, a concentrate outlet 16, and abacksplash outlet 17. It should be noted at this point that FIG. 1 is anelevational cross section view taken along a line 11 of FIG. 3; whereas,FIG. 3 is a crosssectional plan view taken generally along a line 3-3 ofFIG. 1.

As will be more fully explained subsequently, aninfluent, such as stormwater overflow having enormous amounts of water and relatively littlesolids, is fed to the feed pipe 12 and deflected outwardly by theimpinge: ment plate 13 toward the inside of the rotating screen cage 11.The screen cage includes a plurality of screen panels, and the influentis screened resulting in a highly liquid effluent and a concentratewhich is substantially less liquid but flowable. The effluent isdischarged by outlet 15 and the concentrate is discharged by outlet 16.The screen cage 11 is rotated at a speed to provide a suitablecentrifugal force for the screening action, and the impingement plate 13is positioned to provide the desired flow rate of influent toward thescreen cage. A distribution dome 18 may be provided to direct theinfluent as a plurality of substantially discrete inclined flows towardthe inner surface of the screen cage. Influent which splashes back fromthe inner surface of the screen cage may be redirected to the cage formore complete screening, as by collecting the backsplash and recyclingthe same with incoming influent. The upflow of influent provided by thefeed pipe 12 simplifies the design and construction of the apparatus andinvolves less fluid head loss than encountered with a feed of influentto the screen cage from above the apparatus.

These screening concepts serve to reduce pollution caused, for example,by overflow of combined stormsanitary sewage systems during periods ofheavy rain fall. As much as one-third of the sewage solids settle to thebottom of large combined sewers and in periods of heavy rain, they flowinto streams, lakes, rivers and costal waters without treatment. Thus,during storm peaks, up to percent of the untreated sanitary sewage mayoverflow into receiving waters. As a result, combined treatment systemsoften loose more pollutants to their rivers and streams than they takeout in the treatment plant itself.

As will appear from the following description and drawings, the presentapparatus and concepts meet many storm-sanitary pollution controlrequirements for a compact, low cost, high volume, primary treatmentsystem. The present apparatus is capable of releaving a combined sewagesystem of its hydraulic overload during storm periods, while sending apollutant concentrate to the treatment plant. Exemplary apparatus isapproximately 7 feet in diameter and 6 feet high and employsapproximately nine to 18 removable screen panels on a revolving screencage. A combination of high velocity influent flow and centrifugal forcecan allow approximately 90 to 95 percent of a hydraulic flow of 3million gallons per day to pass through the screens. The remainingconcentrate containing a high percentage, such as 99 percent, ofthefloatable and settleable solids is discharged separately into thehydraulically relieved sewage system.

Considering the construction of the apparatus in more detail, thehousing includes a base 20, a substantially cylindrical upstanding wall21, and covers 22 and 23 to provide a substantially closed container.The

screen drive assembly is secured to the top of the ap-- paratus' andincludes a mounting plate 24 for supporting a motor, only the base 25thereof being seen in the drawings, and a gear box 26. Suitable supportand spacing plates 27 through 29 are providedto which an I- beam 30 withgussets 31 and 32 are secured to form a bearing mount. A pair ofbearings 33 and 34 are secured to the bearing mount. A shaft 35 isjournaled in the bearings 33 and 34 and has a drive pulley 36 afflxed atthe upper-end thereof. A pulley 37, as seen in FIG. 2, is coupled withthe output shaft of the gear box 26, and the pulleys 36 and 37 arecoupled by means of V-belts 40 and 41. An idler 42 may be provided tomaintain proper belt tension. As will be apparent to those skilled inthe art, the motor is coupled with the input shaft of the gear box 26 inany suitable manner, as by V-belts,

and drives the shaft 35 through the bear box, pulleys 37 and 36, and theV-belts 40 and41. A collar 43 is secured, as by welding, to the lowerend of the shaft 35,

' and the screen cage 11 is attached to this collar to enable the shaft35 to rotate the screen cage 1 1.

The wall 21 of the housing 10 extends upwardly as indicated at 44. Thecover 22 may be a lift-off cover, and includes windows 45 as seen inFIG. 2 to enable observation of the interior of the apparatus. Aremovable access door cover 46 may be provided. The wall 21 of thehousing 10 may include a window 47 for observation of the interior ofthe apparatus. Suitable bracing is provided within the housing forstructural purposes and for firmly supporting the various pipes. Anangle bracket 48 and braces 49, for example, are provided as illustratedin FIGS. 1 and 3.

The screen cage 11 will be described in more detail subsequently, butgenerally includes a cage formed ofa lower angle ring 50, an upper barring 51, and a plurality of upstanding bars 52 extending between theangle ring 50 and bar ring 51 as best seen in FIGS. 7 and 8. Nine bars52 have been used for an exemplary cage approximately 36 inches indiameter. Support ribs 53 are connected between the various bars 52 anda central collar 54 which is secured to the collar 43 affixed to theshaft 35. Removable screen panels 56 having a frame and screeningmaterial of metal or cloth secured thereto are inserted between thevertical bars 52 and clamped thereto in a substantially sealedrelationship.

As noted earlier, an influent to be screened is supplied through theinfluent pipe 12 and directed upwardly toward the impingement plate 13.The plate deflects the flow outwardly toward the innersurface of thescreen panels 56 of the screen cage 1 l. The vertical position of theplate 13 is adjustable as will be explained subsequently so as tocontrol the rate of flow of influent. The distribution dome 18 as bestseen in FIGS. 1 and 5 is secured to the upper end of the pipe 12. Thisdome 18 includes a sleeve 60 which rests on a collar 61 affized to thepipe 12, and a plurality of inclined plates 62 secured to the outersurface of the sleeve 60. A portion 63 of each plate may be bentupwardly as shown in FIG. 5, or separate spacers may form the portions63, and secured to the underside of the next succeeding plate so as toform a rigid structure. The distribution dome 18 functions to directinfluent, which has been deflected by the impingement plate 13, intosubstantially inclined streams toward the inner surface of the screenpanels. An interior wall or divider 66 which is substantiallycylindrical is secured within the housing and extends almost up to thehorizontal surface of the flange of the angle ring 50. This dividerforms, in combination with the housing wall 21, an annular chamber 67for receiving effluent and directing the same to the effluent outlet 15.The effluent, as is known to those skilled in the art, is the materialwhich passes through the screen cage 11. The divider 66 also encloses aconcentrate chamber or bowl 68 which has an inclined bottom 69 fordirecting concentrate to the concentrate outlet 16.

A back-splash pan 71 is positioned within the chamber 68 and coupledwith a support 72. The pipe 17 communicates with the interior of the pan71. The top of the pan 71 is approximately at the elevation of thebottom of the screen panels and the radius of the upper portion of thepan 71 is slightly smaller than the interior diameter of the screen cage11 so as to receive influent which splashes back from the inner surfaceof the screen cage 11 and screen panels 56. The radius of the pan 71typically may be about 2 inches less than the radius of the screen cage11. Concentrate flows through the gap between the interior of the cageand the exterior of the pan 71 to the chamber 68.

The purpose of the backsplash pan 71 is to enable any influent whichsplashes from the screen cage 11 to be collected for either recyclingwith incoming influent or sent to another separator device for screeningto ensure that the maximum desired split between effluent andconcentrate is achieved. Alternatively, other methods of collectingbacksplash may be provided, as for example a baffle below thedistribution dome 18 which catches or otherwise deflects the backsplashmaterial back toward the inner surface of the screen panels at the lowerportion'of the screen cage 11. In a test with a 2,200 gallon per minuteinfluent flow with no screen panels in the screen cage, it was foundthat 46 gallons of influent was collected in the chamber 68. It isbelieved that this occurred because of backsplash from the screen cagebars 52. By recycling or further screening of this 46 gallons ofbacksplash in a normal operation with screens it has been computed thatthe split would be improved by 2 percent or better.

Turning again to the influent impingement plate 13, the same isadjustable up and down as noted earlier. The purpose of this adjustmentis to enable control of an orifice area 75 between the lower surface ofthe plate 13 and upper end of the sleeve 60 of the distribution dome18-, or upper end of the pipe 12 in the event the same extends above thesleeve 60. Thisallows control of the rate of flow of influent. The plate13 is secured to a rod 76 which extends upwardly through the shaft 35 asseen in FIGS. 1 and 5a and 4b. The upper end of the rod 76 is threadedinto a threaded bushing 77 which is secured to the upper end of theshaft 35. The rod 76 thus may be adjusted up or down to vary theposition of the plate 13 with respect to the upper end of the sleeve 60,and may be locked in position by a locknut 78. With the constructionthus described, the plate 13 rotates with the screen cage 11, but may bemade stationary if desired by other suitable supporting structure. 7

The shape of the plate 13 may be other than flat,

such as a segment of a sphere. However, it is desired that the flows ofinfluent toward the inner surface of the screen cage 1 1 besubstantially perpendicular to the inner surface of the screen panel 56rather than significantly inclined upwardlyor downwardly as viewed inFIG. 1. If these flows are sharply inclined downwardly, the concentrateis excessively liquid; but, on the other hand,-if the flows'areprecisely horizontal and thus perpendicular to the inner surface of thescreen panels the flows do not fan out" sufficiently to give a widesweeping flow onto the inner surface of the screen panels. Accordingly,it is desired that the flow of influent be almost perpendicular to theinner surface of the screen panels but at a slight downward angle toobtain a divergent flow, or fan-out of the flow, by the time theinfluent hits the screen panels. Each flow of influent should fan out toanywhere from substantially the entire height of the screen panels toapproximately onehalf the height of the screen panels, or slightly lesssuch as to provide an impingement area of influent onto the screenpanels'about six inches high. Thus, it is desired that the flows fan-outslightly, but still flow substantially horizontally from the orifice 75,the fanning-out being accomplished by the distribution dome 18 intoessentially discrete inclined streams. If only a portion of the heightof the screen panels is swept by the influent flows, the panels can beturned over end-for-end after a period of use to maximize screen life.

As noted earlier, the majority of the existing combined sewersthroughout the nation do not have adequate capacity during heavy stormperiods to transport all waste and storm-caused combined flows to atreatment facility. The overflow is bypassed to a receiving stream, thuscausing pollution problems. One of the principal applications of thepresent apparatus is in screening enormous amounts of water with solids,such as storm overflow, to separate out the solids and provide arelatively fluid, as distinguished from dry, concentrate which can thenbe properly handled by a sewage treatment facility. The effluent can besuitably disposed of, as for example in a stream. In this manner, theenormous amounts of water do not overtax the sewage treatment facility,while still enabling proper treatment of the maximum amount of solidsfrom the overflow.

One of the principal objectives is to achieve a high split, that is,ratio of effluent (screened product) to concentrate (unscreenedproduct), while still obtaining a slightly fluid concentrate which canflow continuously from the apparatus and be supplied, as by pumping, tosubsequent primary treatment equipment without the problems involved inhandling a solids con-- centrate. A typical ratio is better than 95 to 5with the apparatus described herein and with a typical influent flow ofabout 1000 gallons per minute. A number of factors affect this split,one of the principal factors being the centrifugal force involved in thescreening operation, which varies as the square of the screen cage rpmand as a direct function of the radius thereof. There is a band ofoptimum performance in terms of centrifugal force. It has been foundthat a centrifugal force of around 3 gs appear to be optimum inachieving the maximum split, although it is to be understood that theforce can be below or above this value somewhat. This approximate forceor band around 3 gs can be obtained with a screen cage speed ofapproximately 65 rpm for a screen cage about 60 inches in diameter, andapproximately 88 rpm for a screen cage about 36 inches in diameter.Substantially higher speeds do not improve the split. Additionally,other factors are important in achieving the maximum split, and theseinclude the velocity of the feed of influent, such as approximatelythirteen to fifteen feet per second, which can be selected by varyingthe size of the orifice through adjustment of the plate 13; directing ofthe flows of influent substantially perpendicular to the inner surfaceof the screen cage as noted earlier; recycling or other screening ofbacksplash from 'the screen cage; maintaining the screen panels clean;and the orientation of the screen cloth in the screen panels.

The centrifugal force is important in achieving the maximum force on thesolid and water particles for separation of the water from the solids,but must not be excessive because the solids will then tend to cling tothe screen and bing or clog the screen and, additionally, screen damagemay result from high forces. At the optimum force of band of force, theconcentrate flows by gravity down from the screen. The provision ofalmost perpendicular flows to the inner surface of the screen isimportant as noted earlier so as to achieve the maximum separation withthe minimum of backsplash or other deflection of influent from thescreen cage. As to flow velocity, if the same is too low, insufficientinfluent reaches the screen. If too high, too much influent reaches thescreen and excessive backsplash occurs, and the high forces may causepremature blinding of the screen and/or damage thereto. The backsplashrepresents unscreened influent, much of which is believed to bedeflected from the bars 52 of the screen cage, and it is desiied torecycle or otherwise further screen the backsplash to optimize thesplit. It will be apparent that the screen panels must be clean toachieve the best screening action, and a cycle of influent feed andspray cleaning with a cleaning fluid is preferred as will be describedsubsequently.

The orientation of the screen cloth within the cage is important from awear-life standpoint. It is preferable that the screen cloth be biasmounted to form the screen panels 56 of FIG. 7 rather than positioningthe cloth such that the wires or thread of the screen cloth runvertically and horizontally. The bias mounting disposes the wires orthread at substantially 45 angles resulting in better screen lifebecause the screen wires are stressed and flexed equally and uniformlyby the flows of influent. This longer life allows the screen cage to runlonger with less down-time therefor improving the efficiency ofscreening. Also, the slope of the inclined plates 62 of the distributiondome l8 affects the height of which the flows impinge on the screenpanels and, thus affects screen life. A 6 inch drop at the edge of theplate where the radial length of the plate is 28 inches gives a slope of21 percent which has been found suitable for a 60 inch diameter cage. IFurthermore, it is believed that the direction of rotation of the screencage with respect to the inclination of the plate 62 of the dome 18 maycontribute to obtaining the most efficient screening operation. Thedirection of rotation of the screen cage 11 is preferably as indicatedwith respect to the screen panel '56 illustrated in FIG. (counterclockwise) and as illustrated with respect to the screen cage in FIG. 8.Referring again to FIG. 5, the flows of influent leave the inclinedplates 62 of the distribution dome 60 at substantially the angle of theplates 62 and are believed to aid in sweeping large solid particles fromthe rotating screen.

Screen cleaning is achieved by means of supply pipes 80 and 81 havingrespective groups of nozzles 82 and 83. The nozzles 82 and 83providesprays of cleaning fluid through the screen panels. It ispreferred to feed influent for a period of time, such as 4% minutes to 5minutes, stop the flow of influent and spray the screen panels with acleaning fluid such as a hot water hypochlorite solution for one-fourthto 1 minute, and then continue to feed the influent. This operationcontinues cyclically,'with the cleaning period lasting, for example,one-half minute, with a spray from the nozzles 82 for seconds and thenfrom the nozzles 83 for seconds. It is desired to clean the screensbefore they get dirty which can be measured in terms of degradation ofthe split, for example, down to 90-to-10.

Turning again to the screen cage, and particularly FIGS. 7 through 9,preferably the screen panels 56 are removable for repair or replacement,and can be readily locked in place in the screen cage. Channels forreceiving the edges of the screen panels 56 are provided by T-brack'ets85 which are secured to the bars 52 by threaded stubs 86 and 87 andrespective wing nuts 88 and 89. Braces9l are secured between adjacentribs 53, and a gasket 92 is affixed onto each brace 91 to from a sealwith the top of each respective screen panel 56. The edges of the frame93 of the screen panel 56 which abut with the bars 52 may have a bead ofresilient material 94 thereon to form a seal between the screen panelsand bars 52.v The panel includes an angle frame and the screen fabricmay be secured thereto with an epoxy adhesive. Exemplary screen fabricis 165 TBC providing 47 percent open area. Metal or synthetic fabricscan be used. Stainless steel fabric has been found suitable. A removablecover 95 having a removable section 96 may be provided for the top ofthe screen cage.

A vent pipe 97 may be provided to vent the interior of the housing 10 tothe atmosphere. A plate 98 is attached to the shaft 35 above the coverportions 22 and 23 of the housing. Operation of the screening apparatuscauses a higher pressure area toward the periphery of the screen cage11, and air is drawn in between the plate 98 and'cover portions 22-23and vented by the vent pipe 97. This flow of air past the plate 98 aidsin maintaining the bearings 33 and 34 clean and moisture free. The plate98 prevents material from splashing onto the bearings from the coverportion 22-23 where the shaft 35 extends therethrough.

The following represent exemplary test data from the screening ofinfluent by apparatus like that described and illustrated and employingwhat is referred to as a 36 inch screen cage, the actual inside diameterdefined by the inner surface of the screen panels being approximatelythirty inches. Table IA sets forth data obtained with a large orificeopening; whereas, the data in Table 1B involves variations in theorifice 75.

TABLE IA Feed No. Approx. Average General Test G.P.M. RPM ConcentrateComments 1 1,000 3.3% 26 gpm splashback 2 1,000 0 2.3% No screens-notrotating 3 1,000 0.8% No screens-rotating 4 1,000 60 1.3% No screens 51,000 72 1.2% No screens 6 1,000 93 1.0% No screens 7 1,000 78 1.0% Noscreens 8 1,000 0 2.2% No screens-not rotating 9 1,000 78 1.0% Noscreens 10 1,000 0 12.0% 7-165 TBC panels, 2-165/4 panels 11 1,000 788.6% 7-165 TBC panels, 2 1 65/4 panels 12 1,500 78 13.4% 7-165 TBCpanels, 2-165/4 panels 13 650 78 9.2% 7-165 TBC panels, 2-165/4 panels14 1,000 0 15.0% 7-165 TBC panels, 2-105 Dacron panels 15 1,000 87 8.6%7-165 TBC panels, 2-105 Dacron panels TABLE IB Feed Test Approx. FeedAverage General No. G P M RPM Orifice Concentrate Comments 16 1,000 90V4" 4.3% screens as above-40 ft/sec feed velocity 17 1,000 90 2.0% 15ft/sec velocity =3 gs 1 000 90 I 2 3% cf. 18 u 19 1,000 90 2.2% 20l,000' 90 3/ u E6 T 2.0% 21 1,000 90 V T 2.0% 22 1,000 90 4 2.0% 231,000 90 T 1.93% 24 1,000 90 T 1.76% 25 1 000 90 4+ T 1.67%

l-% T 26 1,000 90 3 T 1.88% 27 1,000 90 /4 +1 1.76% 28 1,000 90 3 1% T2.00% 29 1,000 90 WET 1.71% 30 1,000 120 T 1.67% 31 1,000 60 /s T 2.3%32 1,000 90 13/16" 1.7%

250 PPM Paper Pulp Solution 33 1,000 90 13/16" 5.0% 34 1,000 90 13/16"7.7% (Dirty Screens) Tests 1 through 32 are on a clean water influent,and tests 33 and 34 involve an approximately 250part per million paperpulp solution. As is apparent from Tables IA and 1B, a split of 8.3 to8.6 percent was obtained in tests 1 through 15 on clean water; however,the feed impingement velocity was well under 10 feet per second.Commencing with test No. 16, changes were made in the impintement plate13 adjustment and thus represent performance in terms of concentratesplit at different orifice openings and rpms. The references under thefeed orifice column to +1 turn, l T, and so forth refer to turns of therod 76 which was threaded 9 turns per inch. Test No. 25 represents thebest performance in terms of concentrate split. Test'No. 30 indicatesthat no substantial improvement in split was gained by increasing therpm above 90 rpm. Ninety rpm for this apparatus provides about 3 gs ofcentrifugal force which also has been found to be substantially optimumfor a 60 inch separator unit operating at 65 rpm. Likewise nosubstantial improvement was found in test No. 31 at 60 rpm.

It should be noted that one 124 rpm gives over 6 gs and 60 rpm givesless than 2 gs for the approximately 30 inch diameter screen involved.Although a useful split is obtained, more optimum operation occurs,consistent with maximum screen life and obtaining a slightly wetconcentrate, when the centrifugal force is nearer to 3 gs. However, itis intended herein by reference to approximately 3 gs centrifugal forceto refer to a band of centrifugal force around 3 gs such as one to 7 gs,but preferably closer to 3 gs.

The following Table 1] includes data wherein the influent was rawsewage, and summarizes 14 test runs of the same unit. Initial testsutilizing a 165 fusion bonded four mesh screen indicated a concentratesplit ranging from six to eight percent. Later runs with bias mounted 165 TBC screens indicated a substantial improvement in split as comparedwith the fusion bonded 165/4. Test No. 6 is not believed to berepresentative because the influent was of unusual character. The 165TBC screen panels provided the best performance at approximately 90 rpmas can be seen from Table 11. It should be noted that the concentratevolume in both test Nos. 8 and 9 at the lower 62 rpm increasedsubstantially as compared with the 90 rpm cage speed. Also, test Nos. 10and 1 1 at 124 rpm indicate a wetter concentrate than at 90 rpm. Thescreen was cleaned in a cyclic manner as previously described. It willbe noted that an increase in concentrate split was obtained by using thebias mount 165 TBC screen panels as compared to fusion bonded panels.Similar results in split have been obtained with similar apparatushaving an approximately 60 inch diameter screen cage.

TABLE ll Con- Average Feed trolled Test Approx. Feed Concen- Type of No.G.P.M. RPM Opening Irate Screen 1 1,000 83.5 34" (too short 165/4 fusionbonded screen) 6.0% 2 1,000 83.5 16" 8.0% 165/4 The present embodimentsof this invention are to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than the foregoing description, and all changeswhich come within the meaning and range of equivalency of the claimstherefore are intended to be embraced therein.

What is claimed is:

1. Screening apparatus comprising support means,

a rotary substantially cylindrical screen structure supported by saidsupport means,

drive means coupled with said screen structure for rotating said screenstructure, and

feed means extending into said screen structure for feeding an incomingflow of influent to the inner surface of said screen structure, saidfeed means including a feed pipe extending upwardly into said screenstructure for supplying said influent'and deflector means disposed abovethe upper end of said feed pipe, said end of said feed pipe anddeflector means defining .a substantially annular feed orifice, andmeans for relatively adjusting said deflector means and feed pipe tovary the size of said feed orifice to control the rate of flow ofinfluent toward the inner surface of said screen structure, and saidfeed means including distributor means for directing the influent aroundthe interior of the screen structure.

2. Apparatus as in claim 1 wherein said deflector means is adjustablewith respect to the end of said feed pipe to allow the flow of influentto be adjusted within the range of up to approximately 15 feet persecond.

1. Screening apparatus comprising support means, a rotary substantiallycylindrical screen structure supported by said support means, drivemeans coupled with said screen structure for rotating said screenstructure, and feed means extending into said screen structure forfeeding an incoming flow of influent to the inner surface of said screenstructure, said feed means including a feed pipe extending upwardly intosaid screen structure for supplying said influent and deflector meansdisposed above the upper end of said feed pipe, said end of said feedpipe and deflector means defining a substantially annular feed orifice,and means for relatively adjusting said deflector means and feed pipe tovary the size of said feed orifice to control the rate of flow ofinfluent toward the inner surface of said screen structure, and saidfeed means including distributor means for directing the influent aroundthe interior of the screen structure.
 2. Apparatus as in claim 1 whereinsaid deflector means is adjustable with respect to the end of said feedpipe to allow the flow of influent to be adjusted within the range of upto approximately 15 feet per second.